The invention relates to a turning head, in particular a facing head, essentially comprising a support member which is to be secured to the spindle of a machine tool, having at least one radially extending guide means for a radially adjustable slider carrying a tool, an adjusting rod which is movable coaxially with respect to the support member and which acts on at least one helically toothed rack which is axially movable in the support member, and a toothed bar which is arranged on the slider and which extends in the direction of displacement thereof and whose helical teeth mesh with those of the rack and are inclined at the same angle as the rack teeth with respect to the axis of rotation of the support member.
Known turning heads of this kind have one or generally two sliders which are arranged at positions spaced apart by 180.degree. in the peripheral direction and which are displaceable in opposite directions and which each carry a tool. If the guide means for the sliders are arranged in planes which extend perpendicular to the axis of rotation of the support member, such turning heads are mainly suitable for producing flat end surfaces on workpieces. Such turning heads are then also referred to as facing heads. However, there are also turning heads in which the radially extending guide means are inclined for example at an angle of 60.degree. with respect to the axis of rotation of the support member. Turning heads of this kind are frequently used for copying purposes.
Radial displacement of the sliders is effected, while the turning head is rotating, by means of the adjusting rod which is arranged coaxially in the support member and which acts on the above-mentioned helically toothed racks. Now, it has been found that, at the rotary speeds of 1200 r.p.m. which are generally used to date, a considerable amount of wear occurs at the racks and the toothed bars of the sliders, which co-operate with the racks. This is to be attributed to the fact that not just machining forces but also considerable centrifugal forces act on the sliders, and such forces increase in proportion to outward displacement of the sliders. The sides of the teeth which carry the radially outwardly directed forces are subjected to a very severe degree of wear, which results in a considerable reduction in the accuracy of adjustment of the sliders and thus the accuracy of working of the turning head. Indeed, the wear on the sides of the teeth results in play between the forward and backward movement of the rack and thus also between the radially inwardly or radially outwardly directed movement of the slider. This play results in inaccuracies in the radial adjustment of the sliders, and this is a disadvantage in particular in copying turning operations as in such an operation the direction of movement of the sliders is reversed one or more times during the copying process.
The invention is now based on the problem of providing a turning head, in particular a facing head, of the above-indicated kind, wherein wear of the racks and toothed bars which are provided for displacement of the sliders is reduced or substantially eliminated, without detrimentally affecting the radial adjustment travel of the slider, and while being of compact and simple construction.